The present invention relates to a gasket for an internal combustion engine, more particularly a cylinder head gasket situated between a cylinder head and a cylinder block for tightly sealing therebetween. The cylinder head gasket of the invention is especially useful where cylinder bores of the engine, through which pistons reciprocate, are situated close to each other.
An automobile engine has been developed to become light in weight and small in size as well as to increase power. In association therewith, combustion pressure and heat load applied to an engine increase, so that is has become hard to properly seal between the cylinder head and the cylinder block by means of a conventional cylinder head gasket.
Especially, a large amount of heat load is concentrated in portions between the cylinder bores of the cylinder head gasket. Further, the distance between the cylinder bores has, recently, becomes small because of development of a small engine with light weight. Therefore, it is very difficult to properly seal a portion between the cylinder bores.
A conventional cylinder head gasket 10, as shown in FIG. 1, comprises a main seal member 11 having four cylinder bores 12 and a plurality of holes 13, 14 and 15 for bolts, cooling water and push rods, respectively, and a cover member 16 for covering a part of the main seal member 11 adjacent the cylinder bores 12. The main seal member 11 is formed of a gasket material, such as asbestos, mixture of asbestos and gum, mixture of synthetic fibers and gum, or graphite. The cover member 16 includes four ring members 17, each having upper, bottom and curved portions 18, 19 and 20, respectively (FIGS. 2 and 3). The bottom portions 19 of the ring members 17 are connected to the adjacent bottom portions so that the cover member 16 becomes a single structure (FIG. 1).
In the embodiment as shown in FIGS. 1 and 2, the main seal member 11 includes a core material 21 embedded therein. The cover member 16 is attached to the main seal member 11 so that each curved portion 20 is located inside each cylinder bore 12. In this position, each bottom portion 19 is located under the main seal member 11. The upper portions 18 are bent to be located above the main seal member 11.
In case the cylinder head gasket 10 formed as explained above is installed in a newly developed engine, where the distance between the cylinder bores is made smaller than that in the conventional engine, the gasket material of the main seal member 11 may finally become creep relaxation due to excess heat in use. Consequently, seal pressure on the gasket 10 becomes low to cause gas leakage. If the distance between the cylinder bores are too short, the cylinder head gasket may be broken due to insufficient strength of the gasket.
Another conventional cylinder head gasket 10' is shown in FIG. 3, wherein the gasket 10' further includes a plurality of seal rings 22, each seal ring 22 having a bead 23 therein. The seal rings 22 are placed in the respective cylinder bores 12 of the main seal member 11, and the cover member 16 is installed in the gasket 10' as in the gasket 10, so that the seal rings 22 are held in the gasket 10'. The cylinder bore formed in the seal member 11 of the embodiment 10' is slightly larger than that formed in the embodiment 10. Consequently, the seal rings 22 can be placed in the seal member 11.
In case the cylinder head gasket 10' as explained above is installed in a newly developed engine as in the gasket 10, since the seal rings 22 are independently formed and held by the cover member 16, the gasket 10' can not demonstrate enough strength. Therefore, gas leakage may occur. In an extreme situation, the cover member may be broke.
Accordingly, one object of the present invention is to provide a gasket for an internal combustion engine, wherein the cylinder bores can be properly sealed.
Another object of the present invention is to provide a gasket as explained above, wherein a space between the cylinder bores can be securely sealed.
A further object of the present invention is to provide a gasket as explained above, wherein the gasket can be easily and economically manufactured.
Further objects and advantages of the invention will be apparent from the following description of the invention.